Prior patents providing the background of development in the removal of bitumen from tar sand are:
U.S. Pat. No. 3,941,679--(1976) Smith et al PA0 U.S. Pat. No. 4,120,775--(1978) Murray et al PA0 U.S. Pat. No. 3,856,474--(1974) Pittman et al PA0 U.S. Pat. No. 1,862,945--(1932) Schlotterhose PA0 U.S. Pat. No. 1,024,230--(1912) Turner et al
The patent to Smith utilizes a three stage apparatus for separating hydrocarbonaceous substances from tar sand. The tar sand is first placed in an inclined reactor 20 having auger type conveyor 30 located therein. Solvent from nozzles 28 is sprayed onto the tar sand forming a slurry. The mixture is then conveyed to a second inclined reactor, also having an auger conveyor, where a diluted solvent is sprayed onto the slurry from nozzles 38. The tar sand is then conveyed to a third reactor 26 having an inclined auger conveyor 48. Full strength solvent is sprayed from nozzles 51 onto the tar sand removing the last of the hydrocarbons from the sand. The mixture of solvent and hydrocarbons is withdrawn from the lower end of reactors 24 and 26. The solvent is then distilled and recycled to stages one and three while the remaining bitumen is left to be processed.
Murray describes apparatus for recovering bitumen from tar sand in which the tar sand is fed to an inclined screw conveyor 24 where it is elevated while simultaneously being washed by a liquid hydrocarbon solvent. From the first inclined conveyor the sand is deposited on a second inclined conveyor 30 where steam is applied to wash the remaining solvent from the sand. The mixture of solvent and bitumen is continuously pumped from a conduit C to a centrifuge 14 then to a solvent recovery column 17 where the solvent is distilled and recycled while the bitumen is removed.
Pittman discloses a five stage apparatus for recovering bitumen from tar sand where the tar sand is conveyed by an endless belt 14 past a series of nozzles 26 which spray solvent onto the tar sand as it passes. The mixture of bitumen and solvent falls through holes in the conveyor belt into compartments Q-W. Each compartment Q-W contains an increasingly stronger mixture of solvent and bitumen, Q having the weakest, W the strongest. The mixture cascades from one compartment to the next until the strongest mixture which is in compartment W is withdrawn by a pump through conduit 48 to a collector where the solvent is distilled and recycled while the bitumen is left.
Schlotterhose and Turner show that it is well known in the art of liquid extraction to convey a solid through a series of inclined screw conveyors while simultaneously providing a counter flow of solvent.
The present method and apparatus while utilizing certain known features of this prior art combines them in an entirely novel and unexpected combination providing efficiency in the extraction of bitumen which could not be foreseen by one skilled in the art at minimum cost in view of the maximum recovery of solvent in the closed systems of the present invention for continuous use and recirculation in the apparatus.